Regulated rectifying apparatus



J. A. POTTER 2,577,151

REGULATED RECTIFYING APPARATUS Dec. 4, 1951 Filed Oct. 11, 1949 2 SHEETS-SHEET l ALARM INVENTOR JAMES ADD/501V POTTER ATTORNEY 1 1951 .1. A. POTTER REGULATED RECTIFYING APPARATUS 2 SHEETS -SHEET 2 Filed Oct. 11, 1949 INVENTOR JZMES Aoolso/v Porrm ATTORNEY Patented Dec. 4, 1951 2,577,151 BEGULA'IED ano'rmvmo. APPARATUS James A. Potter, Rutherford, N. 1., assignor Bell Teieplione'Laboi-atories, Incorporated, New York, N. Y., a' corporation of New York Application October 11, 1949, Serial No. 120,748

The present invention relates generally to 12 Claims. (Cl. 321-25) power supply systems, and more particularly, to

regulated direct current power supplies providing constant current output.

In communication systems, a source of direct current is often required and is commonly produced by rectification of an available alternating current source. Such rectiflers may utilize, for example, thermionic discharge tubes or metallic disc rectifiers employing semiconductive materials such as selenium or copper oxide.

In addition, direct current power supply systems are often required to have certain regulating characteristics. By regulating characteristic is meant a control of one or more of the output parameters as the operation of rectifier is varied. For example, in the instance of supplying direct current power to repeater stations remotely located along a communication cable, a constant current output is found desirable. Constant current power supplies have also been found advantageous in the operation of submarine or underwater cable equipment.

In summary, the system employs a rectifier. rectifying current from an alternating supply source. The rectified current is supplied to the load through the space current path of a space current device, the resistance of the space current path being controlled by the load. A circuit is provided including a saturable reactor for controlling the alternating voltage impressed upon the rectifier; the saturable reactor has a saturating winding coupled across the space charge path of the space current device. The object of the invention is to provide a regulated direct current power supply having a substantially constant current output with varying conditions of the load circuit; and to provide means to protect such a constant current power supply against failure of certain of the operating elements.

The invention is described in detail in the following specification.

The invention will be explained with reference to the accompanying drawings, of which:

Fig. 1 shows a schematic diagram of a circuit in accordance with a preferred embodiment of the invention; a

2 shows schematically a modification 01' that portion of the circuit shown in the dotted enclosure of Fig. 1;

Fig. 3 shows a further embodiment of a circuit, according to the invention; and

Fig. 4 is an explanatory circuit diagram of a portion of the circuit according to the invention.

Referring now to the drawings, particularly the rectifier system is composed of a transformer Fig.1: a source of alternating current is supplied to terminals I and 2. This alternating current source is then applied to an autotransformer] having a center tap and a sliding or variable tap 4. 'The variable tap 4 provides a varying voltage between itself and the end terminals of the auto,- transformer. The alternating current supply, as modified in voltage by the autotransformer, is

then supplied from terminal i and the variable tap to a conventional rectifier system.

In the circuit depicted by way of illustration,

5 and a bridge rectifier 6. Transformer! is necessary to supply the proper rectifier output voltage for given alternating current supply line voltages,

and to insulate the alternating supply from the direct current output. Transformer 5. however. may be dispensed with without affecting the operation of the invention. The rectifier 8 may conveniently be of the metallic disc type. Such metallic disc rectifiers ordinarily employ a semiconductive substances as copper oxide or selenium. It will be obvious to those skilled in the art that these rectifiers may also be comprised of vacuum tubes such as thermionic discharge tubes or gaseous discharge tubes.

One of the output vertices of rectifier 6 is coupled to a load circuit 28, in series with a bank oi space current devices and a fixed resistance 8.

' These space current devices may be thermionic discharge of vacuum tubes, and will be called series regulator tubes. Such series regulator tubes 1 are represented in Fig. 1 as being triodes having each a cathode, grid and anode. The series regulator tubes 1 are interconnected in parallel; an appropriate current carrying capacity may be provided by varying their number. In addition, by the use of paralleled tubes, the failure of one tube will not disable the system. The anodes and cathodes of the series regulator tubes 1 must be connected in series with the output vertices of bridge rectifier I in such a manner that a positive polarity is applied at the anode of the series regulator tubes, relative to their cathodes.

Resistance to the passage of load current is developed by the insertion of the series regulator tubes 1; the magnitude of this resistance depends upon the voltage applied to the grids of tubes 1. The current drawn by the load causes a small voltage drop to appear across reistance 8. This voltage drop will be unidirectional, although varying in an amount depending upon the load current drawn. The voltage. drop is applied to the grid-cathode circuit of the discharge tubes I through a direct coupled amplifier I-a. Amplification oi the voltage drop across resistance 8 increases the response of the series regulator. tubes 1. The use of a thermionic discharge tube as a series regulation device is familiar, for example, as shown in United States Patent 2,075,966 to A. W. Vance, issued April 6, 1937.

The apparent resistance introduced by the series regulator tubes 1 in series with the output or the rectifier has been shown to depend upon the load current drawn. For example, an increasing load current will be amplified and will place an increased negative voltage upon the control grids of each 01' the discharge tubes 1. This increased negative bias voltage will increase the apparent resistance introduced by the space current path of the regulator tubes I, and thus tends to reduce the load current to more nearly the desired value. Similarly, a decreasing negative voltage resulting from a decreasing load current will decrease the resistance of the space current path.

It is the output current oi the rectifier to which constaiit current regulation is to be applied. The

control of current will be found satisfactory over the operating limits of the regulator tubes I air: their associated direct current amplifier l-a. operating limits of tubes 1 and amplifier 1-1: are approached, the regulation of load current to a constant value becomes less exact; the change of grid voltage on regulator tubes 1 fails to provide suificient variation in the resistance or the space current path to provide constant current output.

The general plan will be to vary the alternating current input voltage to the rectifier 6 in accordance with the voltage drop experienced across the regulator tubes 1. By varying the alternating current input voltage an appropriate. amount, the output voltage or the rectifier, in turn, may be changed to compensate for load current changes; the load variations for which compensation may be achieved will not longer depend upon-the operating range of the regulator tubes 1 and amplifier 'I-a.

According to the invention, the voltage drop appearing between the cathodes and anodes of the regulator tubes I is applied through a filter comprising a choke 9 and a capacitance I0, to the control winding of a saturable reactor 1 I. Thus. as the regulator tubes I operate over the control range as has been described, a correspondingly varying voltage drop will appear through the filter composed of elements 9 and III to the control winding of saturable reactor II.

The system to control the alternating current input voltage supplied to the rectifier may now be described. The relative position or the previously described variable tap l of autotransformer 3 will ultimately determine the voltage which will be supplied to the primary of transformer 5. For example. if the tap 4 reaches that point on the autotransformer winding connected to supply terminal I, no voltage will be supplied to transformer 6. Conversely, ii the variable tap 4 approaches the pointconnected to terminal 2, full lupply line voltage will be applied to the transi'ormer I.

The variable tap 4 is mechanically positioned by a two-phase electric motor I2 with windings in electrical quadrature. One or these windings II-a has a fixed current applied thereto through. a capacitance I: from one side of the line to the center tap oi the autotransformer 3. Quadrature winding iI-b is coupled between the center tap oi the autotranstormer and the junction of 4 the reactance windings of saturable reactor II and ballast reactor l4. Both windings l2-a and IL-b must be energized to provide rotation of the motor I2;

saturable reactor II has three magnetic paths in parallel, formed by a three-legged core. Two opposed, series-connected reactance windings II-a and II-b are symmetrically displaced about the outside legs of the reactor 1 I core. Windings "-11 and I I-b are, in turn. connected in series with a fixed reactor H; the series combination of reactors II and I4 is connected to .the alternating current supply line. The amount of inductive reactance presented by windings II-a and -17 of reactor II is dependent upon a control winding I l-c magnetically coupled to the middle leg of the reactor and having a unidirectional current flowing therein. This unidirectional current will induce a direct current saturating fiux in the core of the reactance, varying the reluctance and causing the inductive reactance of windings II-a and "-12 to vary in accordance therewith. The series combination of saturable reactor II and reactor ll divide the supply line voltage in accordance with the relative ratio of their impedance. As the reactance of windings I I-a and I I-b varies, their impedance varies, and the relative ratios of alternating voltages thus vary responsive to the control winding II-c.

When the regulatory system is in a quiescent state, the voltage drop appearing across the regulator tubes I will have a given magnitude. The windings of saturable reactor II and ballast reactor Il are so arranged that when this given voltage is applied to the control winding "-0 of the saturable reactor 1 I, the impedance of the reactance windings I I-a. and Il-b of saturable reactor II and the impedance of reactor I4 are substantially equal. The resultant voltage across the reactance windings of saturable reactor I l or reactor It will have subtantially the same vectoral magnitude. When the quiescent condition of the regulatory system provides voltages of equal vectoral magnitude across the reactance windings oi reactors I I and of reactor i4, quadrature winding I2-b has substantially no voltage applied thereto. Both ends of motor winding IZ-b will thus be at a mid-point with respect to the alternating current supply line voltage. On one side of winding I2-b is the mid-point reached between reactance windings of reactor II and reactor H; on the other side, connection is made to the mid-point tap oi autotransformer 3.

When a non-quiescent condition indicative of a load current change occurs in the regulatory system, a new value of voltage drop appears across the regulator tubes 1. This new voltage drop will alter the saturation condition of reactor II and, in turn, will cause the impedance offered by windings I I-a and I I-b to change correspondingly. The relative voltages across windings ll-a and II-b and reactor I4 will no longer be equal and a resulting voltage is supplied to quadrature winding IZ-b. Both windings l2-a and 12-h of the motor I 2 will thus be energized. Capacitance I3 aids in correcting the phase of the current supplied to winding II-a, providing a quadrature relation. Motor I2 now rotates, driving the variable tap 4 to some new position on the winding of autotransiormer 3.

To illustrate the operation of the system according to the invention: it the current drawn by the load is assumed to increase, the regulator tubes 1 will attempt to correct the load current by increasing the apparent resistance offered by approach a point on the autotransformer winding nearer to terminal I, reducing the alternating voltage applied to transformer and thus reducing the resultant output voltage of rectifier 6. The reduction in rectifier output voltage should be an amount appropriate for corresponding reduction of the load current previously assumed as increasing. The operation of the regulatory system as described will continue until the voltage drop across the regulator tubes I again reaches the quiescent value; the regulatory system will then return to a dormant condition.

Assuming now a drop in load current, the reactanee of windings il-a and "-1: increases and the motor rotates in the opposite direction to that previously described; the variable tap 4 will be brought to a point on the winding of autotransformer 3 nearer the terminal 2. This will increase the alternating voltage supplied to transformer 8, causing the desired increase in rectifier output voltage to compensate for the load current drop.

Reactor 3 and capacitance In form part of a filter arrangement. The saturated condition of reactor II and the non-linearity inherent in its operation causes harmonics of the alternating current supply frequency to appear across the windings lI-a and ll-b. These harmonics, especially the third harmonic, would be found reflected to the load through winding ll-c were it not for the filter arrangement comprising 9 and Ill. Capacitance I5 is also employed to remove undesired harmonics of the power line frequency across winding I2-b. It may be desirable to supplement capacitance l5 by providing inductance I S-a in series with IS; a single harmonic, such as the third, of large magnitude can thereby be eliminated. Harmonics tends to cause overheating in the motor l2, interfering with the operation of the regulatory system.

Referring to Fig. 2, a modification of a portion of the circuit shown in the dotted enclosure of Fig. l is here shown. In lieu of the single autotransformer 3 employed in the circuit of Fig. 1, two autotransformers l6 and I! are utilized. As with autotransformer 3, autotransformer i6 is provided with a fixed center tap; both autotransformers l6 and I! have variable taps thereon. A center-tapped reactor [8 is connected between the variable taps of the autotransformers II and l1. Mid-point tap 19 on reactor I 8 is connected to the terminal of transformer 5. Autotransformers l6 and H are connected in parallel across the alternating current supply line. The

two-phase motor i2 and its accompanying ele- I ments are connected to autotransformer I in the same manner as described in relation to autotransformer 3.

A change in output load current results in the operation of two-phase motor 12 in the manner described with reference to the circuit of Fig. 1. However, two-phase motor I2 is now connected to the sliding taps on both autotransformers I3 and i1 and will vary both simultaneously. When transformers I6 and I] are sharing the load equally, the magnetomotive forces induced in the core of the intertransformer reactor I! will oppose and cancel; there will be substantially no 6. resultant flux produced in the core of this reactor. In the event that one or the other of autotransformers l3 and I! should fail in operation, the load current of the rectifier system will pass through one-half of the winding of the reactor 13 and develop a resultant flux in the one. Each half of the winding will then have an alternating voltage developed thereon. If the energizing coil of a relay 23 is placed across onehalf of the reactor winding, the appearance of the alternating voltage across reactor it upon failure of one of the autotransformers I3 and II, will operate relay 20. Operation of relay 2| may be used to close an alarm circuit 2| Failure of one of the autotransformers I! or I! will thereupon give warning.

Referring now to Fig. 3, the alternating current supply is applied from terminals l and 2 to a transformer 5 in series with the windings 22-a and 22-h of reactor 22. As in the case of the circuit shown in Fig. 1, the alternating current supply is rectified by bridge rectifier 6 and supplied through a group of paralleled thermionic discharge tubes 1 or similar space current devices and a resistance 8, to the load 28. Cooperation between elements 5, 6, I and 8 to produce the desired rectified output has been described with reference to Fig. l. The regulator tubes 1 will compensate for variations in load current over an operating range of tubes 1; these variations are reflected, in turn, as varying voltage drops across the anodes and cathodes of the regulator tubes I. As before, these varying voltages are a function of the magnitude of the necessary correction and are utilized to assist the regulator tubes 1 in maintaining constant load current output. The voltage variations are applied through filters 3 and II as previously, and thence to the control winding 23-0 of a saturable reactor 23.

One possible form of construction for reactor 23 employs a three-legged core and correspondingly, three magnetic paths in parallel. Symmetrically displaced about the core are two center-tapped alternating current windings 23-a J and 23-h. These windings are connected together parallel-opposed; the parallel combination is in series with a reactor 24 across the alternating current supply terminals i and 2. Depending upon the relative impedance of reactor 24 and windings 23-a and 23-h of reactor 23, a voltage will be developed across the latter two windings.

Changes in load current will cause voltage drop variations to be produced across the regulator tubes 1, ultimately causing a unidirectional current to flow through the control winding 23-c of transformer 23. This current develops a direct current flux in the core of the reactor 23, changing the magnetic saturation and reluctance thereof. The change in reluctance alters the reactance of the windings 23-a and 23-23. and therefore the voltage appearing thereon.

windings 23-11 and 23-12 are connected to the anodes of a full wave, grid-controlled rectifier comprising thermionic discharge rectifier tubes "-41 and 25-22. The cathodes of these rectifier tubes are connected together and to one side of a control winding 22-c of reactance 22. Reactance 22 has a three-legged core, and three magnetic paths in parallel. Two reactance windings 22-41 and 22-!) are symmetrically displaced about the core on the two outside legs and are connected together in series-opposition. The magnitude of reactance 22 is controlled by a uni directional current fiowing through the control winding 22-c controlling core saturation and recorresponding decrease in'the impedance of these windings: the voltage appearing across windings 2M and 23-!) will be reduced by virtue of the change in impedance ratio between the latterwindings and reactor 24. A rise in the load cur- I rent thus ultimately results in a decrease in the voltage presented to the full wave rectifiers 25-a and..2B-b; the unidirectional current through winding 22-0 is thereupon lowered. As windings 22-a and 22-12 are always connected across the line in series with reactance 24, the quiescent condition'of the regulatory system will produce a given value of current flow through ding 22-c. In the example stated, it is this given value of current which will be diminished by the in-; crease in load. Such a diminishing, in turn, in-

creases'the magnitude of the reactance of windingsz22-a and'22-b. Inasmuch as the primaryof transformer 5 and windings 22-4 and 22-h are connected in series across the line, the voltage across either of these elements will depend upon the ratio of impedances between them. If the impedances of-windings 22-a and22-b increase through an increase in reactance, the voltage presented across the primary of transformer 5 will vdrop. This results in a depression-of the output voltage of the rectifier i and of-the load current, compensatin'g'for the originally assumed increase inload current.

Similarly, a decrease in load current can be shown to decrease the direct current saturation of the coreof transformer 22,thereupon increasiing the output voltage of the full wave rectifiers 25-dand-254i and increasing the direct currentsaturation of-the core of reactance 22. This will, a in turn, increase'the output of 'the bridge rectifier Band the load current, tending to compensate for the decreased output load current.

The output of the full wave rectifier 25-a and 25-bcis also connected to the series combination .of a varistor 26 and a capacitance 21. The junction of the varistor 26 and capacitance 21 is connected through current limiting resistors to the control grids of rectifiers 25-a and zs-p.

Varistor 2i is'a circuit element having a given.

low resistance to the fiow of current in one direction called the forward current, and a relatively high resistance to the flow of current 'in the opposite direction called the back current. Such a varistor may well be composed of a metallic disc rectifier 29 employing a semiconductive material such as selenium, in parallel with a relatively high' value conventional resistance 30. Operation of the varistor is shown in Fig. 4-a and Fig. 4-1); a majority I; of the total current I, in Fig. 4-a, passes through the metallic disc rectifier 29 with little resistance. 'A flow-of current, 12, in Fig. 4-b in the opposite direction, cannot pass through the metallic disc rectifier and must find-its way through the resistance 2|.

Referring again'to Fig. 3, when the varistnr 26 and capacitance 21 are in steady state co'u-- ditions, represented by a constant output offull wave rectifiers 25-a and 25-h, capacltance-21 will have assumed a charging voltage equivalent to the full wave rectifier output voltage." As a result, no voltage will appear across the varistor 26, and the grids of the rectifiers 25-11 and'fl-b will have substantially. zero voltage diil'erence with respect to their cathodes. However, chafi'gsf occur in the output voltage of the rectifiers 25-a and 25-h, resulting from a compensatory signal, in the manner previously described,

the output voltage of the full wave rectifiei." I

should drop, capacitance 21 will seek to discharge a corresponding portion of the voltageappearing across it. This discharge of voltage will establish a current flowing in the forward direction of the varistor 26. As the resistance of the flow of "current in the forward direction of the varistor is small, the condenser 'wil l discharge rapidly, and substantially no voltage will appear between the grids and cathodes of; rectifier tubes 25-11 and 25-h. However, when the voltage rises across the output of'the run.

wave rectifiers, the capacitance 21 will take an increased charge. This increased charge necessitates a back flow of current through the varistor; a period of time dependent uponthe back resistance of the varistor 26, andultimately upon the value of resistance 20 and capacitance 21, will be required to achieve the steady state charge. During the period of time required for charging condenser 21, a negative voltage will appear upon the control grids of rectifiers 25-a' and 25-h, limiting the flow of current through" these rectifiers and thus providing a time lag in the operation of the circuit.

The overall effect of the grid control of the rectifiers 25-0 and 25-12 is to insert a time lag in the operation of the compensating circuits Such a time lag is useful in elimination of oversensitivity 'in the control circuit; oversensitivity results in a hunting" condition; inability of the control system to arrest itself at the quiescent point, the quiescent point being the conditionat which the load current is maintained atfits desired value.

Itis obvious that the scope of the invention.

is not limited to the specific embodiments described, and that the invention may be employed rectifier for rectifying current from an alternating'current supply source, a circuit for trans.-

mitting rectified current from said rectifier toa load, said circuit having two parallel branchpaths through which said rectifiedcurrent istransmitted to the load, one of said branch paths comprising means responsive to the current" supphring stabilized current. to a load. including of alternating current and a series regulating device having a variable resistance responsive to the output current of the rectifier for controlling the said load current, the said circuit comprising a reactive element having a magnetically saturable core, a saturating winding and a variable impedance winding, means to couple the saturating winding of the said reactive element to the variable resistance of the serie regulating device, and means for controlling the magnitude of the source of alternating current applied to the rectifier in accordance with the magnitude of the impedance of the variable impedance winding of the said reactive element.

3. A power supply system according to claim 2 characterized in that the means for controlling the magnitude of the source of alternating current applied to the rectifier comprises a mechanically variable multiratio transformer interposed between the source of alt :rnating current and the rectifier, an electric motor linked mechanically to the said multir'atio transformer, and means to 'supply the electric motor with a source of electric energy responsive to the magnitude of the impedance of the variable impedance winding of the said reactive element.

4. A power supply system according to claim 2 characterized in that the means for controllin the magnitude of the source of alternating current applied to the rectifier comprises a rectifier input transformer having a secondary winding connected to the rectifier and a primary winding, a second reactive element having a magnetically saturable core, a saturable winding and a variable impedance winding, means to couple the variable impedance winding of the said second reactive element in series with the primary of the said transformer to the source of alternating current, an auxiliary rectifier having an input responsive to the variable impedance winding of the first-mentioned reactive element, and means to couple the output of the said auxiliary rectifier to the saturating winding of the said second reactive element.

5. In combination, a rectifier for rectifying current from an alternating current supply source, a circuit for transmitting rectified current from the said rectifier to a load, said circuit comprising an electron discharge path, having a cathode, grid and anode, means to couple the anode-cathode circuit of the said electron discharge path in series with the said circuit, means to derive a control voltage in the grid-cathode circuit of the said electron discharge path proportional to the current supplied to the load, a reactance element having a magnetically saturable core, an impedance winding and a direct current saturation control winding, mean to couple the control winding of the said reactance element in parallel with the said electron discharge path, and means to control the alternating voltage from the said source impressed upon the said rectifier, said latter means being responsive to the magnitude of the impedance of the impedance winding of the said reactive element.

6. In combination, a rectifier for rectifying current from an alternating current supply source, a circuit for transmitting rectified current from the said rectifier to a load, said circuit comprisin: an electron discharge path, having a cathode, grid and anode, means to couple the anodecathode circuit of the said electron discharge path in series with the said circuit, means to derive a control voltage in the grid-cathode circuit of the said electron discharge path proportional to the current supplied to the load, a'reactan'ce element having a magnetically saturable core, an impedance winding and a direct current saturation control winding coupled in parallel with the said electron discharge path, means to derive a, control voltage responsive to the magnitude of the impedance of the impedance winding of the said reactance element, and means to regulate the alternating voltage from the said source impressed on the said rectifier in accordance with the said control voltage.

7. In combination, a main rectifier for rectifying current from an alternating current supply source, a circuit for transmitting rectified current from the said main rectifier to a load, said circuit comprising an electron discharge path, having a cathode, grid and anode, means to couple the anode-cathode circuit of the said electron discharge path in series with the said circuit, means to derive a control voltage in the grid-cathode circuit of the said electron discharge path' proportional to the current supplied to the load, a first saturable reactor having an impedance winding and a direct current saturation control winding coupled in parallel with the said electron discharge path, a fixed reactor connected to the supply source through the impedance windin of the said first saturable reactor, an auxiliary rectifier having it input coupled to the impedance winding of the said first saturable reactor, a second saturable reactor having a direct current control winding and an impedance winding in series with the alternating current supply source to the main rectifier, and means to couple the direct current control winding of the said second saturable reactor to the output 0f the said aux iliary rectifier.

8. In combination, a rectifier for rectifying current from an alternating current supply source, a circuit for transmitting rectified current from the said rectifier to a load, said circuit comprising an electron discharge path, having a cathode, grid and anode, means to couple the anodecathode circuit of the said electron discharge path in series with the said circuit, means to derive a control voltage in the grid-cathode circuit of the said electron discharge path proportional to the current supplied to the load, a mac tor having a magnetically saturable core, a direct current saturation control winding coupled in parallel with the said plurality of thermionic discharge tubes and an impedance winding, means to derive a control voltage responsive to the magnitude of the impedance of the impedance winding of the said reactance element, a variable tap transformer connected between the said rectifier and source of alternating current, an electric servomotor mechanically linked to the said variable tap transformer, and means to excite the said electric servomotor in accordance with the said derived control voltage.

9. In combination, a rectifier for rectifying current from an alternating current supply source, a circuit for transmitting rectified current from the said rectifier to a load, said circuit comprising a plurality of thermionic discharge tubes, having each a cathode, grid and anode, means to couple the anode-cathode circuits of the said thermionic discharge tubes to each other in parallel and together in series with the said circuit, means for deriving and impressing upon the grid-cathode circuit of the said thermionic discharge tubes a control voltage proportional to the current supplied to the load, a saturable reactor having a direct current saturation control ll winding coupled in parallel with the said plurality of thermionic discharge tubes and an impedance winding, a fixed reactor connected to the source of alternating current through the impedance winding of the said saturable reactor, a polyphase motor having winding in quadrature, means to excite one of the windings of the said motor in a given phase, an autotransformer connected between -the said rectifier and the source of alternating current, said autotransformer having a variable tap mechanically linked to the said motor. and means to couple the free winding of the said motor in parallel with the impedance winding of the said reactor, whereby the said motor i excited in quadrature.

10. Apparatus as in claim 9 having a second autotransformer connected between the said rectifier and the source of alternating current, a balancing reactor having portions thereof coupled discretely in series with the said autotransformers, and an alarm relay coupled in parallel with one of the said portions of the balancing reactor.

11. In a constant current, direct current power supply system including a rectifier, a transformer, a source of alternating current supplied to the rectifier through the said transformer, a load coupled to the output of the said rectifier, and a saturable reactor having an impedance winding responsive in magnitude of impedance to variations in the load current, in combination, an auxiliary rectifier comprising at least one thermionic discharge tube having a cathode, grid and anode, means to connect the anode-cathode circuit of the said thermionic discharge tube in series with the impedance winding of the said saturable reactor, a fixed reactor connected to the source of alternating current inseries with the impedance winding of the said saturable reactor, a varistor, a capacitance coupled to the output of the said auxiliary rectifier in series with the said varistor, means to connect the junction of the said varistor and resistance to the control grid of the said thermionic discharge tube. an auxiliary saturable reactor having a direct current control winding and an impedance winding interposed between the alternating current supply and the said transformer, and a coupling of the direct current control winding of the said auxiliary saturable reaction to the output of the said auxiliary rectifier.

12. In a constant current. direct current power supply system including a rectifier, a source of alternating current supplied thereto, a load coupled to the output of the said rectifier, and a saturable reactor having an impedance winding responsive in magnitude of impedance to variations in the load current, in combination, a reactor coupled to the source of alternating current in series with theimpedance winding of the said saturable reactor, a quadrature-wound motor having one winding excited in a given phase, an autotransformer coupled between the source of alternating current and the rectifier, said autotransformer having a variable tap thereon coupled mechanically to the said motor, and means to couple the free winding of the said motor between the junction of the said reactor and .saturable reactor and a point electrically removed with respect to the source of alternating current.

JAMES A. POI'I'ER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PA'I'ENT Drlbrell et a1 Dec. 2, 1947 

